Amplifier



Nov. 16, 1948. w. B. ELLWOOD AMPLI FIER Filed May 16, 1945- FIG.

FIG. 4

FIG. 3

FIG 2 mv- TOR n. 3. ELL WOOD ATTORNEY Patented Nov. 16, 1948 AMPLIFIERWalter B. Ellwood, New York, N. Y., assignor to Bell TelephoneLaboratories, Incorporated, New York, N. Y., a corporation of New YorkApplication May 16, 1945, Serial No. 594,050

6 Claims.

This invention relates to an amplifier circuit and more particularly toa circuit in which relays are employed as active elements to produce anoutput in the form of variable width impulses having a useful componentapproximately proportional to an input which is variable in magnitudeand direction.

An amplifier of this type is most useful for continuous control indriving a reversible load unit such as, for example, a separatelyexcited direct or alternating current motor.

It is therefore the object of the invention to provide an amplifierhaving relays as active elements thereof which is reliable in operation,simple in structure and which has a large gain with good output wattage.

The amplifier in accordance with the present invention may comprise oneor more stages of vacuum tube amplification the output from the laststage of tube amplification being applied to the biasing windings of tworelays in such a manner that the input signal causes the biasing of oneof the relays to increase while the biasing of the other relay decreasesand vice versa. The relays are each supplied with an additionaloperating Winding. The operating windings of the two relays may beconnected in series or in parallel and energized from a source ofalternating or pulsating current, whereby, with no signal present andtherefore no current flowing through the biasing windings of the relays,the relays operate and release in unison at a rate determined by theperiodicity of the alternating or pulsating operating current.

A source of power such as a battery is connected between one contact ofone relay and the corresponding contact of the other relay and two equalresistances are connected in series between the other contacts of therelays. The load circult is connected between the junction of theresistances and the mid-cell tap of the battery so that with both relaysoperating and releasing in unison equal and opposite currents from thetwo sections of the battery are applied to the load circuit with noeffect thereon.

With current of one polarity applied to the biasing windings of therelays a first one of the relays is caused to lead the other inoperation so that for a short period before the other relay operates animpulse is transmitted from only onehalf of the battery to the loadcircuit, theduration of the impulse being dependent upon the amount ofthe lead. Reversely, with current of the opposite polarity applied tothe biasing windings the second of the relays would be caused to leadthe operation of the first relay resulting in the transmission of animpulse from the other half of the battery in the opposite direction tothe load circuit, the duration of the impulse also being dependent uponthe amount of the lead.

For a clearer understanding of the invention reference may be had to thefollowing detailed description to be read in connection with theaccompanying drawing in which:

' Fig. 1 is a circuit diagram illustrating the invention;

Fig. 2 shows curves illustrating the approximate values of the summationof the currents flowing through the windings of both relays when noinput signal is present;

Fig. 3 shows curves illustrating the approximate values of the currentflowing through the operating winding, through the biasing winding andthe summation thereof for each of the relays when biasing current of onepolarity is applied to the biasing windings; and

Fig. 4 shows curves illustrating the approximate values of the currentflowing through the operating Winding, through the biasing winding andthe summation thereof for each of the relays when biasing current of theopposite polarity is applied to the biasing windings.

The load controlling relays A and B and the vibrator relay V of Fig. 1are of the type disclosed in Patent No. 2,289,830 granted to me on July14, 1942. It is to be understood, however, that relays of other typescould be used. Each of these relays as, for example, the relay V,comprises an envelope I of glass or other suitable material which iseither evacuated or filled with an inert gas, or hydrogen, underpressure, a pair of terminals 2 and 3 sealed through the envelope, reedarmatures 4 and 5 of iron or other suitable magnetic material securedwithin the envelope to the inner ends of the terminals 2 and 3 withtheir overlapping ends normally out of engagement and an operating coilor winding 6 outside of and surrounding the envelope. When the winding 6is sufficiently energized from a source of current, the reed armatureswhich lie within the field set up by the winding are attracted intoengagement with each other.

Relays A and B are similar in construction to relay V except that eachof these relays has two windings, relay A having an operating winding 9and a biasing winding l0, and relay B having an operating winding l3 anda biasing winding l4.

The operating windings 9, l3 and 6 of relays A, B and V are connectablein series with the battery 15 by the switch l6. The biasing windings l0and Id of relays A and B are connected in series between the inputterminals W and E8, the windings of the relays being so connected intotheir energizing circuits that when Current is flowing through thebiasing winding M] of relay A and the biasing winding M of relay B insuch a direction as to render windings 9 and ll] of relay A aiding, thwindings I3 and M of relay B are energized in opposition and that whencurrent is flowing through the biasing windings I and I4 in such adirection as to render windings i3 and I 4 aiding, the windings 9 andit) are energized in opposition.

To simplify the disclosure, the battery l3 and potentiometer 2b aredisclosed connected between the input terminals H and if) for supplyingbiasing potential of a desired magnitude and polarity. The potentiometer20 is bridged around the battery I9 with the slider connected to theterminal I! and the mid-cell tap of battery l9 connected to terminal 88.With the slider of the potentiometer 2!] at the mid-tap position on thepotentiometer winding, no current will flow over the circuit through thebiasing windings I El and I 4 of relays A and B but if the slider ismoved toward one end of the potentiometer winding current will fiow inone direction through the biasing windings or if the slider is movedtoward the other end of the potentiometer winding, current will flow inthe other direction through the biasing windings. As previously stated,the input terminals H and I8 could be supplied with biasing potential inany other desired manner as, for example, from the outputs of amplifiertubes.

For creating pulsating current impulses in the operating windings 9 andI 3 of relays A and B, the terminals of the winding 6 of the vibratorrelay V are connected respectively to the terminals 2 and 3 so that whenthe winding 6 becomes fully energized and the reed armatures 4 and 5become attracted into engagement they serve to shortcircuit the winding6 whereby impulses of current having approximately the wave form shownat a in Fig. 2 are transmitted through the operating windings 9 and I3of relays A and B.

The upper contacts I and I i of relays A and B are interconnectedthrough equal resistances 2I and 22 and the lower contacts 8 and I2 ofsuch relays are interconnected through the battery 23. The load 24 isconnected between the junction point 25 of the resistances 2I and 22 andthe midcell tap 26 of the battery 23.

It will first be assumed that the slider of potentiometer 2e is at themid-tap position of the potentiometer winding and that therefore nobiasing current flows through the biasing windings I I] and I4 of relaysA and B. When the switch It is now closed current will flow seriallythrough the operating windings 5% and 53 of relays A and B and throughthe winding 6 of relay V and relay V will become energized to cause theengagement of its reed armatures 41 and 5. Thereupon the winding 6becomes short-circuited and the current flowing through the operatingwindings ll and I 3 of relays A and B increases to a value such thatrelay A causes its reed armatures I and 8 to engage and to therebyestablish a circuit from the negative pole of the left section ofbattery 23 through the load 24, through resistance 2 I, over thearmatures of relay A and to the positive pole of the left section ofbattery 23 and relay B causes its armatures II and I2 to engage and tothereby establish a second circuit from the negative pole of the rightsection of battery 23 over the armatures of relay B, through resistance22 and through the load 24 to the positive terminal of the right sectionof battery 23. It will be noted that the currents flowing through theload 24 from the two sections of battery 23 are equal and opposite. Assoon as the potential stored in the winding 6 of relay B becomesdissipated over the short-circuit through the relay armatures 4 and 5,the armatures disengage and with the coil 6 again included in serieswith the operating windings 9 and E3 of relays A and B, the currentflowing through the windings 9 and i3 decreases to a value below thatrequired to maintain the armatures of such relays engaged and thepreviously traced circuits through the load 24 becomes opened. Since therelays A and B thus simultaneously attract their respective armaturesinto engagement and simultaneously release their armatures out ofengagement, the impulses of opposite polarity which are transmittedthrough the load 24 on each cycle of operation of relays A and Btherefore being of equal duration, no effect on the load 24 is produced.

The curve a shown in Fig. 2 shows the approximate shape of the currentimpulses transmitted through the operating windings of relays A and Bunder the control of the vibrator relay V, the upper curve showing thecurrent through the operating winding of relay A and the lower curveshowing the current through the operating winding of relay B. Since ithas been assumed that there is no biasing current flowing through thebiasing windings of relays A and B the curve also represents thesummation of the currents received by both windings of each relay, thesesummation curves being designated CA and CB in Fig. 2. If it be assumedthat relays A and B will each cause its associated armatures to engagewhen the current value rises to the value represented by the dotted lineOP and will release when the current value drops to the valuerepresented by the dotted line REL then each relay will remain energizedduring the periods represented by the portions 0 of the curve OR and bereleased during the portions R. It will be noted that the length ofthese portions 0 or the length of time the relays are energized areequal for both relays and there fore no eifective current is transmittedto the load as represented by curve P shown between the two portions ofFig. 2.

It will now be assumed that the slider of potentiometer 20 is now movedin a direction to apply biasing current to the biasing winding IE1 ofrelay A which aids the pulsating current impulses applied to theoperating winding ll of this relay and to apply biasing current to thebiasing winding I t of relay B which opposes the pulsating currentimpulses applied to the operating windings I3 of the latter relay.Referring now to Fig. 3 the pulsating currents applied to the operatingwindings 9- and I3 of relays A and B are represented by the curves a.The biasin current applied to the biasing winding Ill of relay A isrepresented by the line b+ in the upper portion of Fig. 3 and thebiasing current applied to the biasing winding 54 of relay B isrepresented by the line bin the lower portion of Fig. 3. The summationof the currents flowing through the two windings of relay A is nowrepresented by the curve CA in the upper portion of Fig. 3 and thesummation of the currents flowing through the two windings of relay B isrepresented by the curve CB in the lower portion of Fig. 3. The portions0 of curve O-R in the upper portion of Fig. 3 now represent the periodsduring which the armatures of relay A remain engaged to apply current ofone polarity to the load 24 and the portions 0 of curve OR in the lowerportion of Fig. 3 represent the periods during which the armatures ofrelay B remain engaged to apply current of the opposite polarity to theload 24. It is to be noted that the durations of the impulsestransmitted by relay A are longer than the durations of the impulsestransmitted by relay B and consequently current will flow in onedirection through the load 24 under the control of relay A during suchperiods as relay B is not at the time energized as represented by theoutput curve P shown between the two portions of Fig. 3.

It will now be assumed that the slider of potentiometer 2D is now movedin a direction to apply biasing current to the biasing winding of relayA which opposes the pulsating current impulses applied to the operatingwinding 9 of such relay and to apply biasing current to the biasingwinding 14 of relay B which aids the pulsating current impulses appliedto the operating winding I 3 of the latter relay. Referring now to Fig.4 the pulsating currents applied to the operating windings 9 and I3 orrelays A and B are represented by the curves a, the biasing currentapplied to the biasing winding 10 of relay A is represented by the lineb in the upper portion of Fig. 4 and the biasing current applied to thebiasing winding M of relay B is represented by the line 13+ in the lowerportion of Fig. 4. The summation of the currents flowing through the twowindings of relay A is now represented by the curve CA in the upperportion of Fig. 4 and the summation of the currents flowing through thetwo windings of relay B is represented by the curve CB in the lowerportion of Fig. 4. The portions of curve O-R in the upper portion ofFig. 4 now represent the periods during which the armatures of relay Aremain engaged to apply current of one polarity to the load 24 and theportions 0 of curve O-R in the lower portion of Fig. 4 represent theperiods during which the armatures of relay B remain engaged to applycurrent of the opposite polarity to the load 24. It is to be noted thatthe durations of the impulses transmitted by relay B are longer than thedurations of the impulses transmitted by the relay A and consequentlycurrent will flow in a direction through the load opposite to thatpreviously discussed in connection with the consideration of Fig. 3 asrepresented by curve P shown between the two portions of Fig. 4.

It will thus be seen that impulses of current will be applied to theload 24 in a direction which is dependent upon the direction of bias ofthe input current applied between the input terminals l1 and I8 and theduration of such impulses will depend upon the magnitude of the biasingcurrent.

While the operating windings of relays A and B are disclosed asenergized by pulsating current impulses generated through the action ofthe vibrator relay V, it will be apparent that such windings could beenergized by a combination of alternating and direct current or byalternating current. As illustrated, the load 2-4 is represented by abox labeled load. This load obviously could be in a device which mightbe designed to operate by impulses of one or the opposite polarity suchas, for example, the armature circuit of a direct current motor thefield of which is separately excited.

What is claimed is:

1. In an amplifier circuit, two relays, means for applying a current ofperiodically varying amplitude in the same phase relationship to saidrelays whereby said relays are caused to operate in phase, an inputcircuit for applying a biasing current in opposite phase relationship tosaid relays respectively, means for varying the direction of saidbiasing current, a source of power, a load device, and means controlledin response to the operation of said relays for applying power from saidsource to said load device, the application of said biasing current tosaid relays being effective to shift the phase relationship between theoperating times of said relays whereby the direction of the impulsestransmitted from said source to said load device is made dependent uponthe direction of the phase shift.

2. In anamplifier circuit, two relays, means for applying a current ofperiodically varying amplitude in the same phase relationship to saidrelays whereby said relays .are caused to operate in phase, an inputcircuit for applying a biasing current in opposite phase relationship tosaid relays respectively, means for varying the magnitude of the biasingcurrent, a source of power, a load device, and means controlled inresponse to the operation of said relays for applying power from saidsource to said load device, the application of said biasing current tosaid relays being efiective to shift the phase relationship between theoperating times of said relays whereby the duration of each impulsetransmitted from said source to said load device is made dependent uponthe magnitude of the biasing current.

3. In an amplifier circuit, two relays, means for applying a current ofperiodically varying amplitude in the same phase relationship to saidrelays whereby said relays are caused to operate in phase, an inputcircuit for applying a biasing current in opposite phase relationship tosaid relays respectively, means for varying the direction and magnitudeof said biasing current, a source of power, a load device, and meanscontrolled in response to the operation of said relays for applyingpower from said source to said load device, the application of saidbiasing current to said relays being efiective to shift the phaserelationship between the operating times of said relays whereby thedirection of the impulses transmitted from said source to said loaddevice is made dependent upon the direction of the phase shift and theduration of each impulse is made dependent upon the amount of the phaseshift.

4. In an amplifier circuit, two relays each having an operating and abiasing winding, means for applying a current of varying amplitude inthe same phase relationship to said operating windings whereby said.relays are caused to operate in phase, an input circuit for applying abiasing current in opposite phase relationship to said biasing windingsrespectively, means for varying the direction and magnitude of saidbiasing current, a source of power, a load device, and

means controlled in response to the operation of said relays forapplying power from said source to said load device, the energization ofsaid biasing windings being effective to shift the phase relationshipbetween the operating times of said relays whereby the direction of theimpulses transmitted from said source to said load device is madedependent upon the direction of the phase shift and the duration of eachimpulse is made dependent upon the amount of the phase shift.

5. In an amplifier circuit, two relays each having an operating and abiasing winding, means including a source of current and a vibratorrelay for applying a current of varying amplitude in the same phaserelationship to said operating windings whereby said relays are causedto operate in phase, an input circuit for applying a biasing current inopposite phase relationship to said biasing windings respectively, meansfor varying the direction and magnitude of said biasing current, asource of power, a load device, and means controlled in response to theoperation of said relays for applying power from said source to saidload device, the energization of said biasing windings being effectiveto shift the phase relationship between the operating times of saidrelays whereby the direction of the impulses transmitted from saidsource to said load device is made dependent upon the direction of thephase shift and the duration of each impulse is made dependent upon theamount of the phase shift.

6. In an amplifier circuit, two relays each having an operating and abiasing winding, means including a source of current and a selfshuntingvibrator relay connected in series with said operating windings forapplying a current of varying amplitude in the same phase relationshipto said operating windings whereby said relays are caused to operate inphase, an input circuit for applying a biasing current in opposite phaserelationship to said biasing windings respectively, means for varyingthe direction and magnitude of said biasing current, a source of power,a load device, and means controlled in response to the operation of saidrelays for applying power from said source to said load device, theenergization of said biasing windings being effective to shift the phaserelationship between the operating times of said relays whereby thedirection of the impulses transmitted from said source of power to saidload device is made dependent upon the direction of the phase shift andthe duration of each impulse is made dependent upon the amount of thephase shift. WALTER B. ELLWOOD.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,858,267 Eames May 1'7, 19322,156,534 Hyland May 2, 1939 2,371,415 Tolson Mar. 13, 1945

